function largeestNumber(arr) {
    var new_str = [];
    for(let i=0;i<arr.length;i++){
        arr[i].sort(function (a,b) {
            return b-a;
        });
        new_str.push(arr[i][0]);
    }
    return new_str;
}


console.log(largeestNumber([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]));